Black holes…quarks…dark matter. It seems like the cosmos gets a little stranger every year. Until recently, the astronomical universe known to humans was populated by planets, stars, galaxies, and scattered nebulae of dust and gas. Now, theoretists tell us it may also be inhabited by objects such as superstrings, dark matter and massive neutrinos — objects that have yet to be discovered if they exist at all!
As bizarre as these new constituents may sound, you don’t have to be a rocket scientist to appreciate the most mysterious ingredient of them all. It is the inky blackness of space itself that commands our attention as we look at the night sky; not the sparse points of light that signal the presence of widely scattered matter.

During the last few decades, physicists and astronomers have begun to recognize that the notion of empty space presents greater subtleties than had ever before been considered. Space is not merely a passive vessel to be filled by matter and radiation, but is a dynamic, physical entity in its own right.

One chapter in the story of our new conception of space begins with a famous theoretical mistake made nearly 75 years ago that now seems to have taken on a life of its own.

In 1917, Albert Einstein tried to use his newly developed theory of general relativity to describe the shape and evolution of the universe. The prevailing idea at the time was that the universe was static and unchanging. Einstein had fully expected general relativity to support this view, but, surprisingly, it did not. The inexorable force of gravity pulling on every speck of matter demanded that the universe collapse under its own weight.

His remedy for this dilemma was to add a new ‘antigravity’ term to his original equations. It enabled his mathematical universe to appear as permanent and invariable as the real one. This term, usually written as an uppercase Greek lambda, is called the ‘cosmological constant’. It has exactly the same value everywhere in the universe, delicately chosen to offset the tendency toward gravitational collapse at every point in space.

A simple thought experiment may help illustrate the nature of Lambda. Take a cubic meter of space and remove all matter and radiation from it. Most of us would agree that this is a perfect vacuum. But, like a ghost in the night, the cosmological constant would still be there. So, empty space is not really empty at all — Lambda gives it a peculiar ‘latent energy’. In other words, even Nothing is Something!

Einstein’s fudged solution remained unchallenged until 1922 when the Russian mathematician Alexander Friedmann began producing compelling cosmological models based on Einstein’s equations but without the extra quantity. Soon thereafter, theorists closely examining Einstein’s model discovered that, like a pencil balanced on its point, it was unstable to collapse or expansion. Later the same decade, Mount Wilson astronomer Edwin P. Hubble found direct observational evidence that the universe is not static, but expanding.

All this ment that the motivation for introducing the cosmological constant seemed contrived. Admitting his blunder, Einstein retracted Lambda in 1932. At first this seemed to end the debate about its existence. Yet decades later, despite the great physicist’s disavowal, Lambda keeps turning up in cosmologists’ discussions about the origin, evolution, and fate of the universe.

THEORY MEETS OBSERVATION

Friedmann’s standard ‘Big Bang’ model without a cosmological constant predicts that the age of the universe, t0, and its expansion rate (represented by the Hubble parameter, H0) are related by the equation t0 = 2/3H0. Some astronomers favor a value of H0 near 50 kilometers per second per megaparsec (one megaparsec equals 3.26 million light years). But the weight of the observational evidence seems to be tipping the balance towards a value near 100. In the Friedmann model, this implies that the cosmos can be no more than 7 billion years old. Yet some of our galaxy’s globular clusters have ages estimated by independent methods of between 12 and 18 billion years!

In what’s called the Einstein-DeSitter cosmology, the Lambda term helps to resolve this discrepancy. Now a large value for the Hubble parameter can be attributed in part to “cosmic repulsion”. This changes the relationship between t0 and H0, so that for a given size, the universe is older than predicted by the Friedmann model.

In one formulation of Einstein’s equation, Lambda is expressed in units of matter density. This means we can ask how the cosmological constant, if it exists at all, compares with the density of the universe in the forms of stars and galaxies.

So far, a careful look at the available astronomical data has produced only upper limits to the magnitude of Lambda. These vary over a considerable range – from about 10 percent of ordinary matter density to several times that density.

The cosmological constant can also leave its mark on the properties of gravitational lenses and faint galaxies. One of the remarkable features of Einstein’s theory of general relativity is its prediction that space and time become deformed or ‘warped’ in the vicinity of a massive body such as a planet, star or even a galaxy. Light rays passing through such regions of warped “space-time” have their paths altered. In the cosmological arena, nearby galaxies can deflect and distort the images of more distant galaxies behind them. Sometimes, the images of these distant galaxies can appear as multiple images surrounding the nearby ‘lensing’ galaxy.

At Kyoto University M. Fukugita and his coworkers predicted that more faint galaxies and gravitational lenses will be detected than in a Friedmann universe if Lambda is more than a few times the matter density. Edwin Turner, an astrophysicist at Princeton University also reviewed the existing, scant, data on gravitational lenses and found that they were as numerous as expected for Lambda less that a few times the matter density. By the best astronomical reconning, Lambda is probably not larger than the observed average matter density of the universe. For that matter, no convincing evidence is available to suggest that Lambda is not exactly equal to zero. So why not just dismiss it as an unnecessary complication? Because the cosmological constant is no longer, strictly, a construct of theoretical cosmology.

NOTHING AND EVERYTHING

To understand how our universe came into existence, and how its various ingredients have evolved, we must delve deeply into the fundamental constituents of matter and the forces that dictate how it will interact. This means that the questions we will have to ask will have more to do with physics than astronomy. Soon after the big bang, the universe was at such a high temperature and density that only the details of matter’s composition (quarks, electrons etc) and how they interact via the four fundamental forces of nature were important. They represented the most complex collections of matter in existence, long before atoms, planets, stars and galaxies had arrived on the scene.

For two decades now, physicists have been attempting to unify the forces and particles that make up our world – to find a common mathematical description that encompasses them all. Some think that such a Theory of Everything is just within reach. It would account not only for the known forms of matter, but also for the fundamental interactions among them: gravity, electromagnetism, and the strong and weak nuclear forces.

These unification theories are known by a variety of names: grand unification theory, supersymmetry theory and superstring theory. Their basic claim is that Nature operates according to a small set of simple rules called symmetries.

The concept of symmetry is at least as old as the civilization of ancient Greece, whos art and archetecture are masterworks of simplicity and balance. Geometers have known for a long time that a simple cube can be rotated 90 degrees without changing its outward appearance. In two dimensions, equalateral triangles look the same when they are rotated by 120 degrees. These are examples of the geometric concept of Rotation Symmetry.

There are parallels to geometric symmetry in the way that various physical phenomena and qualities of matter express themselves as well. For example, the well-known principle of the Conservation of Energy is a consequence of the fact that when some collections of matter and energy are examined at different times, they each have precisely the same total energy, just as a cube looks the same when it is rotated in space by a prescribed amount. Symmetry under a ‘shift in time’ is as closely related to the Conservation of Energy as is the symmetry of a cube when rotated by 90 degrees.

Among other things, symmetries of Nature dictate the strengths and ranges of the natural forces and the properties of the particles they act upon. Although Nature’s symmetries are hidden in today’s cold world, they reveal themselves at very high temperatures and can be studied in modern particle accelerators.

The real goal in unification theory is actually two-fold: not only to uncover and describe the underlying symmetries of the world, but to find physical mechanisms for ‘breaking’ them at low energy. After all, we live in a complex world filled with a diversity of particles and forces, not a bland world with one kind of force and one kind of particle!

Theoreticians working on this problem are often forced to add terms to their equations that represent entirely new fields in Nature. The concept of a field was invented by mathematicians to express how a particular quantity may vary from point to point in space. Physicists since the 18th century have adopted this idea to describe quantitatively how forces such as gravity and magnetism change at different distances from a body.

The interactions of these fields with quarks, electrons and other particles cause symmetries to break down. These fields are usually very different than those we already know about. The much sought after Higgs boson field, for example, was introduced by Sheldon Glashow, Abdus Salam and Steven Weinberg in their unified theory of the electromagnetic and weak nuclear forces.

Prior to their work, the weak force causing certain particles to decay, and the electromagnetic force responsible for the attraction between charged particles and the motion of compass needles, were both considered to be distinct forces in nature. By combining their mathematical descriptions into a common language, they showed that this distinction was not fundamental to the forces at all! A new field in nature called the Higgs field makes these two forces act differently at low temperature. But at temperatures above 1000 trillion degrees, the weak and electromagnetic forces become virtually identical in the way that they affect matter. The corresponding particles called the Higgs Boson not only cause the symmetry between the electromagnetic and weak forces to be broken at low temperature, but they are also responsible for confiring the property of mass on particles such as the electrons and the quarks!

There is, however a price that must be paid for introducing new fields into the mathematical machinery. Not only do they break symmetries, but they can also give the vacuum state an enormous latent energy that, curiously, behaves just like Lambda in cosmological models.

The embarrassment of having to resurrect the obsolete quantity Lambda is compounded when unification theories are used to predict its value. Instead of being at best a vanishingly minor ingredient to the universe, the predicted values are in some instances 10 to the power of 120 times greater than even the most generous astronomical upper limits!

It is an unpleasant fact of life for physicists that the best candidates for the Theory of Everything always have to be fine-tuned to get rid of their undesirable cosmological consequences. Without proper adjustment, these candidates may give correct predictions in the microscopic world of particle physics, but predict a universe which on its largest scales looks very different from the one we inhabit.

Like a messenger from the depths of time, the smallness – or absence – of the cosmological constant today is telling us something important about how to craft a correct Theory of Everything. It is a signpost of the way Nature’s symmetries are broken at low energy, and a nagging reminder that our understanding of the physical world is still incomplete in some fundamental way.

A LIKELY STORY

Most physicists expect the Theory of Everything will describe gravity the same way we now describe matter and the strong, weak and electromagnetic forces – in the language of quantum mechanics. Gravity is, after all, just another force in Nature. So far this has proven elusive, due in part to the sheer complexity of the equations of general relativity. Scientists since Einstein have described gravity ( as well as space and time) in purely geometric terms. Thus we speak of gravity as the “curvature of space-time”.

To acheive complete unification, the dialects of quantum matter and geometric space have to be combined into a single language. Matter appears to be rather precisely described in terms of the language of quantum mechanics. Quarks and electrons exchange force-carrying particles such as photons and gluons and thereby feel the electromagnetic and strong nuclear forces. But, gravity is described by Einstein’s theory of general relativity as a purely geometric phenomenon. These geometric ideas of curvature and the dimensionality of space have nothing to do with quantum mechanics.

To unify these two great foundations of physics, a common language must be found. This new language will take some getting used to. In it, the distinction between matter and space dissolves away and is lost completely; matter becomes a geometric phenomenon, and at the same time, space becomes an exotic form of matter.

Beginning with work on a quantum theory of gravity by John Wheeler and Bryce DeWitt in the 1960’s, and continuing with the so-called superstring theory of John Schwartz and Michael Green in the 1980’s, a primitive version of such a ‘quantum-geometric’ language is emerging. Not surprisingly, it borrows many ideas from ordinary quantum mechanics.

A basic concept in quantum mechanics is that every system of elementary particles is defined by a mathematical quantity called a wave function. This function can be used, for example, to predict the probability of finding an electron at a particular place and time within an atom. Rather than a single quantity, the wave function is actually a sum over an infinite number of factors or ‘states’, each representing a possible measurement outcome. Only one of these states can be observed at a time.

By direct analogy, in quantum gravitation, the geometry of space-time, whether flat or curved, is only one of an infinite variety of geometric shapes for space-time, and therefore the universe. All of these possibilities are described as separate states in the wave function for the universe.

But what determines the probability that the universe will have the particular geometry we now observe out of the infinitude of others? In quantum mechanics, the likelihood that an electron is located somewhere within an atom is determined by the external electric field acting on it. That field is usually provided by the protons in the atomic nucleus. Could there be some mysterious field ‘outside’ our universe that determines its probability?

According to Cambridge University theorist Stephen Hawking, this is the wrong way to look at the problem. Unlike the electron acted upon by protons, our universe is completely self-contained. It requires no outside conditions or fields to help define its probability. The likelihood that our universe looks the way it does depends only on the strengths of the fields within it.

Among these internal fields, there may even be ones that we haven’t yet discovered. Could the cosmological constant be the fingerprint in our universe of a new ‘hidden’ field in Nature? This new field could affect the likelihood of our universe just as a kettle of soup may contain unknown ingredients although we can still precisely determine the kettle’s mass.

A series of mathematical considerations led Hawking to deduce that the weaker the hidden field becomes, the smaller will be the value we observe for the cosmological constant, and surprisingly, the more likely will be the current geometry of the universe.

This, in turn, implies that if Lambda were big enough to measure by astronomers in the first place, our universe would be an improbable one. Philosophically, this may not trouble those who see our cosmos as absolutely unique, but in a world seemingly ruled by probability, a counter view is also possible. There may, in fact, exist an infinite number of universes, but only a minority of them have the correct blend of physical laws and physical conditions resembling our life-nurturing one.

Hawking continued his line of speculation by suggesting that, if at the so-called Planck scale of 10 to the power of -33 centimeters the cosmos could be thought of as an effervescent landscape, or “space-time foam”, then perhaps a natural mechanism could exist for eliminating the cosmological constant for good.

One of the curiosities of combining the speed of light and Newton’s constant of gravitation from general relativity, with Planck’s constant from quantum mechanics, is that they can be made to define unique values for length, time and energy. Physicists believe that at these Planck scales represented by 10 to the power of -33 centimeters and 10 to the power of -43 seconds, general relativity and quantum mechanics blend together to become a single, comprehensive theory of the physical world: The Theory Of Everything. The energy associated with this unification, 10 to the power of 19 billion electron volts, is almost unimaginably big by the standards of modern technology.

The universe itself, soon after the Big Bang, must also have passed through such scales of space, time and energy during its first instants of existence. Cosmologists refer to this period as the Planck Era. It marks the earliest times that physicists are able to explore the universe’s physical state without having a complete Theory of Everything to guide them.

WORMHOLES

Harvard University physicist Sidney Coleman has recently pursued this thought to a possible conclusion. Instead of some mysterious new field in Nature, maybe the Lambda term appears in our theories because we are using the wrong starting model for the geometry of space at the Planck scale.

Previous thinking on the structure of space-time had assumed that it behaved in some sense like a smooth rubber sheet. Under the action of matter and energy, space-time could be deformed into a variety of shapes, each a possible geometric state for the universe. Nearly all candidates for the Theory of Everything’s embed their fields and symmetries in such a smooth geometrical arena.

But what if space-time were far more complicated? One possibility is that ‘wormholes’ exist, filling space-time with a network of tunnels. The fabric of space-time may have more in common with a piece of Swiss cheese than with a smooth rubber sheet.

According to Coleman, the addition of wormholes to space-time means that, like the ripples from many stones tossed into a pond, one geometric state for the universe could interfere with another. The most likely states ( or the biggest ripples) would win out. The mathematics suggest that quantum wormhole interference at the Planck scale makes universes with cosmological constants other than zero exceedingly unlikely.

How big would wormholes have to be to have such dramatic repurcussions? Surprisingly, the calculations suggest that small is beautiful. Wormholes the size of dogs and planets would be very rare. Universes containing even a few of them would exist with a vanishingly low probability. But wormholes smaller than 10 to the power of -33 centimeters could be everywhere. A volume the size of a sugar cube might be teeming with uncounted trillions of them flashing in and out of existence!

Coleman proposes that the action of these previously ignored mini- wormholes upon the geometric fabric of the universe that forces Lambda to be almost exactly zero. Like quantum ‘Pac Men’, they gobble up all the latent energy of space-time that would otherwise have appeared to us in the form of a measureable cosmological constant!

The addition of wormholes to the description of space-time admits the possibility that our universe did not spring into being aloof and independent, but was influenced by how other space-times had already evolved – ghostly mathematical universes with which we can never communicate directly.

The most likely of these universes had Lambda near zero, and it is these states that beat out all other contenders. In a bizarre form of quantum democracy, our universe may have been forced to follow the majority, evolving into the high probability state we now observe, without a detectable cosmological constant.

EPILOG

Wormholes? Wave functions? Hidden fields? The answer to the cosmological constant’s smallness, or absence, seems to recede into the farthest reaches of abstract thinking, faster than most of us can catch up.

As ingenious as these new ideas may seem, the final pages in this unusual story have probably not been written, especially since we can’t put any of these ideas to a direct test. It is a tribute to Einstein’s genius that even his ‘biggest blunder’ made near the beginning of this century still plagues physicists and astronomers as we prepare to enter the 21st century. Who would ever have thought that something that may not even exist would lead to such enormous problems!

The Big Bang theory says that the entire universe was created in a tremendous explosion about 20 billion years ago. The enormity of this event is hard to grasp and it seems natural to ask ourselves ‘What was it like then?’ and ‘What happened before the Big Bang?’. To try to answer these queries, lets take a brief journey backwards in time.
We first see the formation of our own sun about 15 billion years after the Big Bang and then by 5 billion years, the formation of the first galaxies. By 700,000 years, the universe is awash with the fireball radiation that keeps all matter at a temperature of 4,000 degrees. Because of this, darkness is completely absent since every point in the sky glows with the brilliance of the sun. No stars, planets or even dust grains exist, just a hot dense plasma of electrons, protons and helium nuclei. By 3 minutes, we see helium form from the fusion of hydrogen atoms while the universe seeths at a temperature of nearly 1 billion degrees. The average density of matter is that of lead. By 1 second, the Lepton Era ends and the ratio of neutrons to protons has become fixed at 1 neutron for every 5 protons. The temperature is now 5 billion degrees everywhere. At about .0001 second, we watch as the Quark Era ends and the temperature of the fireball radiation rises to an incredable 1 trillion degrees. Quarks, for the first time, can combine in groups of two and three to become neutrons, protons and other types of heavy particles. The universe is now packed with matter as densly as the nucleus of an atom. A mountain like Mt. Everest could be squeezed into a volume no greater than the size of a golf ball!

By 1 billionth of a second, the temperature is 1 thousand trillion degrees and we see the electromagnetic and weak forces merge into one force. The density of the universe has increased to the point where the entire earth could be contained in a thimble. Quarks and anti-quarks are no longer confined inside of particles like neutrons and protons but are now part of a superheated plasma of unbound particles. As the remaining history of the universe unfolds, a long period seems to pass when nothing really new happens. Then, at a time 10(-35) second after the Big Bang, a spectac ular change in the size of the universe occurs. This is the GUT Era when the strong nuclear force becomes distinguishable from the weak and electromagnetic forces. The temperature is an incredable 10 thousand trillion trillion degrees and the density of matter has sored to nearly 10(75) gm/cm3. This number is so enormous that even our analogies are almost beyond comprehension. At these densities, the entire Milky Way galaxy could easily be stuffed into a volume no larger than a single hydrogen atom! Electrons and quarks together with their anti-particles, were the major constituents of matter and very massive particles called Leptoquark Bosons caused the quarks to decay into electrons and vice versa. If we now move forward in time we would witness the vacuum of space undergoing a ‘phase transition’ from a higher energy state to a lower energy state. This is analogous to a ball rolling down the side of a mountain and coming to rest in the lowest valley. As the universe ‘rolls down hill’ it begins a brief but stupendous period of expansion. The universe swells to billions of times its former size in almost no time at all.

In addition to this, a slight excess of matter over anti-matter appears becaus of the decay of massive particles called X Higgs Bosons. As we continue to watch the universe age, the remaining pairs of particles and anti-particles find themselves and vanish in a tremendous burst of annihilation. From this paroxysm, the bulk of the fireball radiation that we now observe is born.

The GUT Era is the last stop in our fanciful journey through time. If we had asked what it was like before the GUT Era, we would immediately have entered a vast no mans land where few indisputable facts would serve to gui de us. What does seem clear is that gravity is destined to grow in importance, eventually becoming the dominant force acting between parti cles, even at the microscopic level.

G R A V I T Y

According to theories developed since the 1930’s, what we call a ‘force’ is actually a collective phenomenon caused by the exchange of innumerable, force-carrying particles called gauge bosons. The electromagnetic force, which causes like charges to attract and dissimilar ones to repel, is transmitted by gauge bosons called photons, the strong force that binds nucleii together is transmitted by gluons and the weak force which causes particles to decay is transmitted by the, recently discovered, W and Z Intermediate Vector Bosons. In an analogous way, physicists believe that gravity is transmitted by particles called Gravitons. If gravity really does have such a quantum property, its effects should appear once quarks and electrons can be forced to within 10(-33) centimeter of one another, a distance called the Planck length. To acheive these conditions, quarks and electrons will have to be collided at energies of 10(19) GeV. An accelerator patterned after the 2-mile, Stanford Linear Accelerator would have to be 1 light-year in length to push particles to these incredable energies! Fortunatly, what humans find impossible to do, Nature with its infinite resources finds less difficult. Before the universe was 10(-43) second old, matter routinely experienced collisions at these energies. This period is what we call the Planck Era.

THROUGH A LOOKING GLASS, DARKLEY

Since our technology will not allow us to physically reproduce the conditions during these ancient times, we must use our mathematical theories of how matter behaves to mentally explore what the universe was like then. We know that the appearence of the universe before 10(-43) second can only be adequatly described by modifying the Big Bang theory because this theory is, in turn, based on the General Theory of Relativity. General Relativity tells us how gravity operates on the macroscopic scale of planets, stars and galaxies. At the Planck scale, we need to extend General Relativity so that it includes not only the macroscopic properties of gravity but also is microscopic characteristics as well. The theory of ‘Quantum Gravity’ is still far from completion but physicists tend to agree that, at the very least, Quantum Gravity must combine the conceptual elements of the two great theories of modern physics: General Relativity and Quantum Mechanics.

In the language of General Relativity, gravity is a consequence of the deformati on of space caused by the presence of matter and energy. Gravity is just another name for the amount of curvature in the geometry of 3-dimensional space. In Quantum Gravity theory, gravity is produced by massless gravitons so that gravitons now represent individual packages of curved space that travel through space at the speed of light.

The appearence and dissappearence of innumerable gravitons gives the geometry of space a very lumpy and dynamic appearance. John Wheeler at Princeton University thinks of this as a foamy, sub-structure to space where the geometry of space twists and contorts so that far flung regions of space may suddenly find themselves connected by ‘wormholes’ which constantly appear and dissappear within 10(-43) seconds. Even as you are reading this article, this frenetic activity is occurring in the hyper-microscopic domain, 100 billion billion times smaller than the nucleus of an atom. For a comparison, the size of the sun and the size of a single atom stand in about this same proportion. Although Quantum Gravity effects are completely undetectable today at the atomic and nuclear scale, during the Planck Era, macroscopic and microscopic worlds merged and the Quantum Gravity of the microcosm suddenly became the Quantum Cosmology of the macrocosm!

QUANTUM COSMOLOGY

As we approach the end of the Planck Era, the random appearance and dissappearance of innumerable gravitons will eventually force us to give up the concept of a specific geometry to 3-dimensional space. Instead, the geometry at a given moment will have to be thought of as an average over all 3-dimensional space geometries that are possible. Once again, the reason for this is that particles are squeezed so closely together that we can now see individual gravitons moving around in the space between them causing space to become curved. We can no longer get away with saying that the space between two quarks, for example, is flat. This is what we mean when we say that the gravitational force between them is insignificant when compared to the other three forces of Nature.

To make matters much worse, not only will Quantum Gravity not allow us to calculate the exact 3-dimensional geometry to space but, at the Planck scale, it will not allow us to simultaneously determine its exact geometry and precise rate of change in time. What this means is that we may never be able to calculate with any certainty exactly what the history of the universe was like before 10-43 second. Today, the large-scale geometry of space is one of three possible types: flat and infinite, negatively curved and infinite or positively curved and finite. During the Planck Era, the ‘large-scale’ geometry was contorted by wormholes and and infinite number of possibilities were possible. To probe the history of the universe then would be like trying to trace your ancestral roots if every human being on earth had a possibility of being one of your parents. Now try to trace your family tree back a few generations! The farther back in time you go, the greater are the number of possible ancestors you could have had. An entirely new conception of what we mea n by ‘a history for the universe’ will have to be developed. Even the concepts of space and time will have to be completely re-evaluated in the face of the qua ntum fluctuations of spacetime at the Planck Era!

THE BIRTH OF THE UNIVERSE

The picture that seems to emerge from using our sketchy outline of what Quantum Gravity theory might look like is that as we approach the Planck Era, gravitons are exchanged between quarks and electrons with increasingly higher energy and in greater number. By the time we reach the end of the Planck Era at 10(-43) second, gravitons will begin to carry as much energy as the other force carriers (Gluons, IVBs and Photons). At still earlier times, a period of complet e symmetry and unification between all the natural forces will ensue. Only one super-unified force exists here (gravity) and only one kind of particle dominates the activity of this age(Gravitons).

During the early 70’s, the Russian physicists Ya. Zel’dovitch and A. Starobinski of the USSR Academy of Science proposed that the rapidly changing geometry of space during the Planck Era may actually have created all the matter, anti-matter and radiation that existed soon after Creation. In their picture of Creation, the rapidly changing geometry of space created particles and anti-particles with masses of 10(19) GeV. This production of matter and anti-matter removed energy from the enormous fluctuations occuring in the geometry of space and eventually succeeded in damping them out altogether by the end of the Planck Era. They also found that the rate of particle creation increased as more and more particles were created.

Several recent studies by Physicists Edward Tryon of Hunter College, R. Brout, F. Englert and E. Gunzig of the University of Brussels and david Atkatz and Heinz Pagels of the Rockefeller University have shed additional light on what Creation may have been like. Imagine if you can, nothing at all! This is the primordial vacuum of space. There is complete darkness here, no light yet exists. The number of dimensions to space was probably not the normal 3 that we are so accustomed to but may have been as high as 11 according to Supergravity theory! In this infinite emptiness, random fluctuations occurred that ever so slightly changed the energy of the vacuum at various points in space. Eventually, one of these fluctuations attained a critical energy and began to grow. As it grew, very massive particles called leptoquarks and anti-leptoquarks were created, causing the expansion to accelerate. This is much like a ball rolling down a hill that moves slowly at first and then gains momentum. The expansion of the proto-universe, in turn, caused still more leptoquarks to be created. This furious cycle continued until, at long last, the leptoquarks decayed into quarks, leptons (electrons, muons etc) and their anti-particles and the universe emerged from the Planck Era. Particle creation stopped once the fluctuations in the geometry of space subsided.

So, we are left with the remarkable possibility that, in the beginning, there ex isted quite literally, nothing at all and from it emerged nearly all of the matter and radiation that we now see. This process has been described by the physicist Frank Wilczyk at the University of California, Santa Barbara by saying, ” The reason that there is something instead of nothing is that nothing is unstable”. A ball sitting on the summit of a steep hill needs but the slightest tap to set it in motion. A random fluctuation in space was apparently all that was required to unleash the incredable latent energy of the vacuum, thus creating matter and energy and an expanding universe from ‘nothing at all’.

The universe did not spring into being instantaneously but was created a little bit at a time in a ‘bootstrap’ process. Once a few particles were created by quantum fluctuations of the empty vacuum, it became easier for a few more to appear and so, in a rapidly escalating process, the universe gushed forth from nothingness.

How long did this take? The primordial vacuum could have existed for an eternity before the particular fluctuation that gave rise to our universe happened. Physicist Edward Tryon expresses this best by saying that ” Our universe is simply one of those things that happens from time to time”.

The principles of Quantum Gravity may ultimatly force us to reconsider questions like ‘What happened before the Big Bang?’ because they imply the existence of something (time) that may not have any meaning at all. These questions may be as empty of meaning as an explorer on the north pole asking, ‘Which way is North?’. Only the complete theory of Quantum Gravity may tell us how to ask the right questions!

Written by Sten Odenwald. Copyright (C) 1995 Sky Publishing Corporation. See February 1996 issue.
THE NIGHT SKY, when you think about it, is one of the strangest sights imaginable. The pinpoint stars that catch your eye are all but swallowed up by the black nothingness of space – an entity billions of light-years deep with which we here on Earth have no direct ex- perience.
What is empty space, really? At first the question seems silly. There’s nothing to it! But look again in light of what modern physics knows and suspects, and the nature of space emerges as one of the most important “sleeper” issues growing for the last 50 years. “Nature abhors a vacuum,” proclaimed Aristotle more than 2,300 years ago. Today physicists are discovering that this is true in ways the ancient Greeks could never have imagined.

True, the cosmos consists overwhelmingly of vacuum. Yet vacuum itself is proving not to be empty at all. It is much more complex than most people would guess. “But surely,” you might ask, “if you take a container and remove everything from inside it – every atom, every photon – there will be nothing left?” Not by a long shot. Since the 1920s physicists have recognized that on a microscopic scale, the vacuum itself is alive with activity. Moreover, this network of activity may extend right down to include the very structure of space-time itself. The fine structure of the vacuum may ultimately hold the keys to some of the deepest questions facing physics – from why elementary particles have the properties they do, to the cause of the Big Bang and the likelihood of other universes outside our own.

THINGS THAT GO BUMP IN THE DARK

The state of the art in physics – our deepest current understanding of the world – is embodied in the so-called Standard Model, in which all matter and forces are accounted for by an astonishingly few types of particles (see Sky & Telescope – December 1987, page 582). Six quarks and six leptons make up all possible forms of matter. In practice just two of the quarks (the up and down) and one lepton (the electron) account for everything in the world except for a few whiffs of exotica known only to high-energy physicists. The 12 particles of matter (and their 12 corresponding particles of antimatter, or antiparticles) are acted upon by “messenger particles” that carry all the known forces. The photon mediates the electromagnetic force, including all the familiar chemical and structural forces around us on Earth. The members of the gluon family carry the strong force that binds neutrons and protons together in atomic nuclei. The W’, W-, and Zo mediate the weak nuclear force, and the as-yet-undiscovered graviton is believed to carry the force of gravity.

Every possible event involving the 12 matter particles can be completely explained as an exchange of messenger particles. During some of these events, for example when electrons accelerate in a radio-transmitter antenna, messenger particles (in this case photons) materialize and travel through space. At other times, however, the messengers remain almost entirely hidden within the interacting system. When the messengers exist in this hidden form, they are called “virtual particles.” Virtual particles may seem ghostly and unreal by everyday standards. But real they are. Moreover, they are not limited to their role of mediating interactions. Virtual particles can also pop in and out of empty space all by themselves.

Quantum mechanics, the rulebook of the Standard Model, states as a bedrock principle that you need a certain length of time to measure a particle’s energy or mass to a given degree of accuracy. The shorter the observation time, the more uncertain the measurement. If the time is very brief, the uncertainty becomes larger than the particie’s entire mass, and you cannot say whether or not the particle is there at all. The lighter the particle, the longer its uncertainty time. In the case of an electron-positron pair, the uncertainty time scale is about 10^-21″ seconds.

On time scales shorter than this, virtual electrons and positrons can, and do, pop in and out of nothingness like peas in a shell game. It’s as if, just because you can’t say a particle doesn’t exist when you look very briefly, then in a sense it does. This is not mere theorizing. In 1958 a tabletop experiment demonstrated the “Casimir effect,” measuring the force caused by virtual particles appearing and vanishing in total vacuum through the attraction they caused between two parallel metal plates. If the vacuum were truly empty the plates should not have attracted, but the incessant dance of virtual particles in the space between them produces a detectable effect.

Every particle – matter as well as messenger – seems to display a virtual form, each seething in greater or lesser abundances in what physicists call the “physical vacuum.” When it comes to affecting the ordinary world, moreover, virtual particles may do much more than just mediate forces. Some, in fact, may cause matter to have the property we call mass. The electron is the simplest of matter particles. Our knowledge of the physical world rests upon a solid understanding of its properties. Yet despite its abundance in the circuitry around us, the electron harbors an enigma. The fact that it has mass cannot be explained in the Standard Model, at least the parts of it that have been experimentally verified. More than 30 years ago particle physicist Peter Higgs suggested that the existence of mass has to do with a new ingredient of nature that is now called the Higgs field, which provides a new type of messenger particle that interacts with the electron to make it “weigh.”

The Higgs field has yet to be discovered, but many physicists expect it to exist everywhere in the physical vacuum, ensuring through its interactions with electrons and other particles that they will display mass. Even now, particle accelerators at CERN in Switzerland and at Fermilab near Chicago are straining at their maximum capabilities to cause just one “Higgs boson,” the presumed messenger particle for this field, to break loose from the vacuum and leave a detectable trace. Success would provide a triumphant completion of the Standard Model.

So to answer our question about whether a container of empty space is truly empty, the best anyone can do is remove the normal, physical particles that nature allows us to see and manipulate. The virtual particles can never be evicted. And in addition there may exist the ever-present Higgs field.

QUANTUM GRAVITY

For most of this century, physicists have struggled to bring gravity into the scheme of forces that are mediated by virtual messenger particles. To put this another way, the theory of general relativity, which shows the force of gravity to be a curvature of space-time, needs to be integrated with quantum mechanics, which shows forces to be virtual particle exchanges. Working on the assumption that such a marriage is possible, physicists named gravity’s messenger particle the graviton. But general relativity requires that gravitons be more than just quanta of gravity. In essence, gravitons define the structure of space-time itself.

The reconciliation of quantum mechanics and general relativity may lead us to dramatically new notions of the nature of space and time. Some theorists have suggested that points in space-time become defined only when a particle (such as a graviton or photon) interacts with other particles. In this view, what they are doing between interactions is a nonphysical question, since only an interaction defines a measurable time and place. Gravitational forces (and thus gravitons) exert an influence at distances much larger than the subatomic realm, as anyone who has fallen down a flight of stairs can attest. But only at an extremely small scale – the Planck length of 10^-33 centimeters – does the quantum nature of gravity become important.

Suppose you could magically look through a microscope that magnified an atomic nucleus to be some 10 light-years across. Under this magnification the smallest gravitons – that is, the most energetic and massive ones – would be about a millimeter in size. Here we might see a strange world in which space-time itself was defined by gravitons intersecting and looping around each other. In a similar vein, Roger Penrose has suggested that the gravitational field and space-time are built up from still more primitive mathematical entities called twistors, and that “ultimately the [space-time] concept may possibly be eliminated from the basis of physical theory altogether.” In essence, space and time become factored out as less- than-fundamental parts of the physical world.

In such a view, only the interactions between twistors, or perhaps gravitons, define when and where space-time is and is not. Are there gaps in the physical vacuum, voids of true and absolute nothing where space and time themselves do not exist?

Another viewpoint on the structure of space-time is offered by “superstring theory.” String theories posit that the fundamental objects of nature are one-dimensional lines rather than points; the “elementary” particles we measure are only oscillations of these strings. Superstring theory only seems to work, however, if space-time has not just four dimensions (three of space and one of time), but 10 dimensions. This hardly seems like the world we live in. To hide the extra six dimensions, mathematicians roll them up into conceptual corners that go by such cryptic names as “Calabi-Yau manifolds” and “orbifold space.” A recent textbook on the subject concludes on a wistful note that “if the string idea is correct, we may never catch more than a glimpse of the full ex- tent of reality.”

More recently, theorists Carlo Rovelli (University of Pittsburgh) and Lee Smolin (Pennsylvania State University) completed their analysis of a quantum gravity model developed by Abhay Ashtekar at Syracuse University in 1985. Unlike string theory, Ashtekar’s work applies only to gravity. However, it posits that at the Planck scale, space-time dissolves into a network of “loops” that are held together by knots. Somewhat like a chain-mail coat used by knights of yore, space-time resembles a fabric fashioned in four dimensions from these tiny one-dimensional loops and knots of energy.

Is this the way the world really is on its most fundamental level, or have mathematicians become detached from reality? Superstring theory has enticed physicists for over a decade now because it hints at a super unification of all four fundamental forces of nature. But it remains frustratingly hard to plant anchors down from these cloud castles into the real world of observation and experiment. The famous remark that superstring theory is “a piece of 21st- century physics that accidentally fell into the 20th century” captures both the excitement and frustration of workers stuck with 20th-century tools.

Surprisingly, string theory, Ashtekar’s loopy space-time, and twistors are not entirely independent ways of looking at space-time. In 1986 theorists discovered that superstrings have some things in common with twistors. A deep connection had been uncovered between two very different, independent theories. Like two teams of tunnelers starting on opposite sides of a mountain, they had met at the middle – a sign, perhaps, that they are dealing with a single real mountain, not separate ones in their own imaginations. And in 1995 Rovelli and Smolin also found that their graviton loops are very closely related to both the twistors and superstrings, though not identical in all respects.

THE COSMIC CONNECTION

Space-time could be strange in other ways too. Theorist John A. Wheeler (In- stitute for Advanced Study) has long advocated that at the Planck scale, space-time has a complex shape that changes from instant to instant. Wheeler called his picture “space-time foam” – a sea of quantum black holes and worm holes appearing and vanishing on a time scale of about 10^-43″ seconds. This is the Planck time, the time it takes light to cross the Planck length. Shorter than that, time, like space, presumably cannot exist – or, at least, our everyday notions of them cease to be valid.

Wheeler’s idea of space-time foam is a natural extrapolation from the idea of virtual particles. According to quantum mechanics, the higher the energy and mass of a particle, the smaller it must appear. A virtual particle as small as 10^-33″ cm, lasting only 10^-43 second, has so great a mass (10^-5 gram) in such a tiny volume that its own surface gravity would give it an escape velocity greater than the speed of light. In other words, it is a tiny black hole. But a black hole is not an ordinary object sitting in space- time like a particle; it is a structure of distorted, convoluted space-time itself. Although the consequences of such phe- nomena are not understood, it is rea- sonable to assume that these virtual par- ticles dramatically distort all space-time at the Planck scale.

If we take this reasoning at face value, and consider the decades-old experiments proving that the virtual particle phenomenon in a vacuum is real, it is hard to believe that space-time is smooth at or below the Planck scale. Space must be broken up and quantized. The only question is how. Wheeler’s original idea of space-time foam is especially potent because according to recent proposals by Sidney Coleman (Harvard) and Stephen Hawking (Cambridge University), its worm holes not only connect different points very close together within our space-time, but connect our space-time to other universes that, as far as we are concerned, exist only as ghostly probabilities. These connections to other universes cause the so-called cosmological constant – an annoying intrusion into the equations of cosmology ever since Einstein (see Sky & Telescope- April 1991, page 362) – to neatly vanish within our own universe.

Space-time foam has also been implicated as the spawning ground for baby universes. In several theories explaining the cause of the Big Bang and what came before, big bangs can bud off from a previously existing space-time, break away completely while still microscopic, and inflate with matter to become new universes of their own, completely disconnected (“disjoint”) from their space- time of origin. This process, proposed by Alan Guth (MIT) and others, gives a handle on what many expect to be another key issue of 21st-century physics: was our Big Bang unique? Or was it just a routine spinoff of natural processes happening all the time in some larger, outside realm? (see Sky & Telescope- September 1988, page 253).

Yet there are problems. The amount of latent energy in the quantum fluctuations of space-time foam is staggering: 10^105 ergs per cubic centimeter. This amounts to 10 billion billion times the mass of all the galaxies in the observ- able universe – packed into every cubic centimeter! Fortunately, Mother Nature seems to have devised some means of exactly canceling out this phenomenon to an accuracy of about 120 decimal places. The problem is that we haven’t a clue how.

It’s unnerving to think that in the 16 inches separating this page from your eyes, new big bangs are perhaps being spawned out and away from our quiet space-time every instant. By comparison, it seems positively dull that the photons by which you see this page might be playing a hop-scotch game to avoid gaps where space-time doesn’t exist.

REALITY CHECK

Some physicists have begun to throw cold water on these fantastic ideas. For instance, in 1993 Matt Visser (Washington University) studied the mathematical properties of quantum worm holes and discovered that, once they are formed, they become stable: they can’t foam at all. Kazuo Ghoroku (Fukuoka Institute of Technology, Japan) also found that quantum worm holes become stable even when their interactions with other fields are considered. What Wheeler called space-time foam may be something else entirely.

Among the unresolved problems facing theorists is the nature of time, which has been recognized as inextricably bound up with space ever since Einstein posited a constant speed for light. In general relativity, it isn’t always obvious how to define what we mean by time, especially at the Planck scale where time seems to lose its conventional meaning. Central to any quantum theory is the concept of measurement, but what does this imply for physics at the Planck scale, which sets an ultimate limit to the possibility of measurement? How any of these ideas about space- time can be tested is currently unknown. Some physicists believe this makes these ideas not real scientific inquiry at all. And it’s worth remembering that mathematics can sometimes introduce concepts that are only a means to an end and have no independent reality.

In the abstract world of mathematical symbolism, it isn’t always clear what is real and what’s not. For example, when we do long division on paper to divide 54,162 by 2 to get 27,081, we generate the intermediate numbers 14, 16, and 2, which we then just throw away. Are virtual particles, compact 6-dimensional manifolds, and twistors simply nonphysical means to an end – mere artifacts of how we humans do our mathematics? Particle physicists often have to deal with “ghost fields” that are simply the temporary scaffolding used for calculations, and that vanish when the calculations are complete. Nonphysical devices such as negative probability and faster- than-light tachyon particles are grudgingly tolerated so long as they disappear before the final answers. Even in super- string theory, recent work suggests that it may be possible to build consistent models entirely within ordinary four-dimensional space-time, without recourse to higher dimensions.

ANGEL FOOD CAKE

So, how should we think of the great, dark void that we gaze into at night? All clues point to space-time being a kind of layer cake of busy phenomena on the submicroscopic scale. The topmost layer contains the quarks and electrons comprising ordinary matter, scattered here and there like raisins in the frosting. These raisins can be plucked away to make a region of space appear empty. The frosting itself consists of virtual particles, primarily those carrying the electromagnetic, weak, and strong forces, filling the vacuum with incessant activity that can never be switched off. Their quantum comings and goings may completely fill space-time so that no points are ever really missing. This layer of the cake of “empty space” seems pretty well established by laboratory experiment.

Beneath this layer we have the domain of the putative Higgs field. No matter where the electron and quark “raisins” go, in this view, there is always a piece of the Higgs field nearby to affect them and give them mass. Below the Higgs layer there may exist other layers, representing fields we have yet to discover. But eventually we arrive at the lowest stratum, that of the gravitational field. There is more of this field wherever mass is present in the layers above it, but there is no place where it is entirely absent. This layer recalls the Babylonian Great Turtle that carried the universe on its back. Without it, all the other layers above would vanish into nothingness.

We know that space-time is quite smooth down to at least the scale of the electron, 10^-20 cm – 10 million times smaller than an atomic nucleus. This is the size limit set for any internal component of the electron, based on careful comparisons between experiment and the predictions of quantum electrodynamics. But near the Planck horizon of 10^-33 cm, space-time must change its structure drastically. It may be a world in which conventional notions of dimensionality, time, and space need to be redefined and possibly eliminated altogether.

The conceit of our universe’s uniqueness may disappear, with big bangs becoming viewed as run-of-the-mill events in some much larger outside realm, and with physical constants being attributed to causes in space-times forever beyond human experience.

There is much that’s spooky about the physical vacuum. This spookiness may be rooted more in the way our brains work than in some objective aspect of nature. Einstein stressed, “Space and time are not conditions in which we live, but modes in which we think.” Our understanding of space remains in its infancy. With Aristotle smiling at us down the centuries, we now see the vacuum as much more than a vacancy. It will take many decades, if not centuries, before a complete understanding of it is fashioned. In the meantime, enjoy the nighttime view!

FURTHER READING

Davies, Paul. The New Physics. Cambridge: Cambridge University Press, 1989.

For 45 years I have followed the great pageant of ideas in theoretical physics. From high school through retirement, although my career and expertise is in astronomy and astrophysics, my passion has always been in following the glorious ideas that have swirled around in theoretical physics. I watched as the quark theory of the 1960s gave way to Grand Unification Theory in the 1970s, and then to string theory and inflationary cosmology in the 1980s. I was thrilled by how these ideas could be applied to understanding the earliest moments in the Big Bang and perhaps let me catch at least a mathematical glimpse of how the universe, time and space came to be literally out of Nothing; explanations not forthcoming from within Einstein’s theory of general relativity.

Even as recently as 2012 this story continued to captivate me even as I grappled with what might be the premature end of my life at the hands of non-Hodgkins Lymphoma diagnosed in 2008. And still I read the journal articles, watching as new ideas emerged, built upon the theoretical successes of the 1990s and beyond. But then a strange thing happened.

In the 1980s, the US embarked on the construction in Texas of the Superconducting Super Collider, but that project was scrapped and de-funded by Congress after ¼ of it had been built. Attention then turned to the European Large Hadron Collider project, which after 10 years finally achieved its first collisions in 2009. The energy of this accelerator has steadily been increased to 13 TeV, and now records some 600 million collisions per second, which generates 30 petabytes of data per year. Among these collisions were expected to be the traces of ‘new physics’, and physicists were not dissappointed. In 2012 the elusive Higgs Boson was detected some 50 years after it was predicted to exist. It was a major discovery that signaled we were definitely on the right track in verifying the Standard Model. But since then, following many more years of searching among the debris of trillions of collisions, all we continue to see are the successful predictions of the Standard Model confirmed again and again with only a few caveats.

Typically, physicists push experiments to ever-higher degrees of accuracy to uncover where our current theoretical model predictions are becoming thread-bare, revealing signs of new phenomena or particles, hence the term ‘new physics’. Theoreticians then use this anomalous data to extend known ideas into a larger arena, and always select new ideas that are the simplest-possible extensions of the older ideas. But sometimes you have to incorporate entirely new ideas. This happened when Einstein developed relativity, which was a ‘beautiful’ extension of the older and simpler Newtonian Physics. Ultimately it is the data that leads the way, and if not available, we get to argue over whose theory is more mathematically beautiful or elegant.

Today we have one such elegant contender for extending the Standard Model that involves a new symmetry in Nature called supersymmetry. Discovered mathematically in the mid-1970s, it showed how the particles in the Standard Model that account for matter (quarks, electrons) are related to the force-carrying particles (e.g. photons, gluons), but also offered an integrated role for gravity as a new kind of force-particle. The hitch was that to make the mathematics work so that it did not answer ‘infinity’ every time you did a calculation, you had to add a whole new family of super-heavy particles to the list of elementary particles. Many versions of ‘Minimally Supersymmetric Standard Models’ or MSSM’s were possible, but most agreed that starting at a mass of about 1000 times that of a proton (1 TeV), you would start to see the smallest of these particles as ‘low-hanging fruit’, like the tip of an upside-down pyramid.

For the last seven years of LHC operation, using a variety of techniques and sophisticated detectors, absolutely no sign of supersymmetry has yet to be found. In April, 2017 at the Moriond Conference, physicists with the ATLAS Experiment at CERN presented their first results examining the combined 2015 – 2016 LHC data. This new dataset was almost three times larger than what was available at the last major particle physics conference held in 2016. Searches for the supersymmetric partners to quarks and gluons (called squarks and gluinos) turned up nothing below a mass of 2 TeV. There was no evidence for exotic supersymmetric matter at masses below 6 TeV, and no heavy partner to the W-boson was found below 5 TeV.

Perhaps the worst result for me as an astronomer is for dark matter. The MSSM model, the simplest extension of the Standard Model with supersymmetry, predicted the existence of several very low mass particles called neutralinos. When added to cosmological models, neutralinos seem to account for the existence of dark matter, which occupies 27% of the gravitating stuff in the universe and controls the movement of ordinary matter as it forms galaxies and stars. MSSM gives astronomers a tidy way to explain dark matter and closes the book on what it is likely to be. Unfortunately the LHC has found no evidence for light-weight neutralinos at their expected MSSM mass ranges. (see for example https://arxiv.org/abs/1608.00872 or https://arxiv.org/abs/1605.04608)

Of course the searches will continue as the LHC remains our best tool for exploring these energies well into the 2030s. But if past is prologue, the news isn’t very promising. Typically the greatest discoveries of any new technology are made within the first decade of operation. The LHC is well on its way to ending its first decade with ‘only’ the Higgs boson as a prize. It was fully intended that the LHC would have given us hard evidence by now for literally dozens of new super-heavy particles, and a definitive candidate for dark matter to clean up the cosmological inventory.

So this is my reason for feeling sad. If the Higgs boson is a guide, it may take us several more decades and a whole new and expensive LHC replacement to find something significant to affirm our current ‘beautiful’ ideas about the physical nature of the universe. Supersymmetry may still play a role in this but it will be hard to attract a new generation of young physicists to its search if Nature continues to withhold so much as a hint we are on the right theoretical track.

If supersymmetry falls string theory, which hinges on supersymmetry, may also have to be put aside or re-thought. Nature seems to favor simple theories over complex ones so are the current string theories with supersymmetry really the simplest ones?

Thousands of physicists have toiled over these ideas since the 1970s. In the past, such a herculean effort usually won-out with Nature rewarding the tedious intellectual work, and some vestiges of the effort being salvaged for the new theory. I find it hard to believe that will not again be the case this time, but as I prepare for retirement I am realizing that I may not be around to see this final vindication.

So what should I make of my 45-year intellectual obsession to keep up with this research? Given what I know today would I have done things differently? Would I have taught fewer classes on this subject, or written fewer articles for popular science magazines?

Absolutely not!

I have thoroughly enjoyed the thrill of the new ideas about matter, space, time and dimension. The Multiverse idea offered me a new way of experiencing my place in ‘reality’. I could never have invented these amazing ideas on my own, which have entertained me for most of my professional life. Even today’s Nature seems to have handed us something new: Gravity waves have been detected after a 60-year search; detailed studies of the cosmic ‘fireball’ radiation are giving us hints to the earliest moments in the Big Bang; and of course we have discovered THOUSANDS of new planets.

Living in this new world seems almost as intellectually stimulating, and now offer me more immediate returns on my investment in the years remaining.

Protons are the work horses of chemistry. Their numbers determine which element you are talking about, and their positive charge determines how many electrons will form a cloud around them to facilitate all manner of chemical reactions.

For decades we thought that protons were absolutely fundamental particles along with neutrons and electrons, but then came the quantum revolution of the 1920s and the escalating quest to understand what their actual physical properties were. Through experimentation, we found that protons all had exactly the same mass to many decimal places. They all had exactly +1.0000 unit of charge, also to many decimal places. But they also possessed an entirely new physical quantity found only in atomic-scale physics. This quantity was called ‘spin’ but had nothing to do with the motion of a top about its axis, although paradoxically it could nonetheless be interpreted in that way.

Quantum spin, unlike the continuous spinning of a top, comes only in integer units like 0, 1, 2, etc, or in half-integer units like ½, 3/2, 5/2 etc. Physicists soon discovered that fundamental particles like photons ( the carriers of light energy) only had a quantum spin of exactly 1.0, while protons, neutrons, neutrinos and electrons had exactly ½ unit of spin. The former kinds of particles were called bosons while the latter were given the name fermions. Composite particles made up from these elementary bosons and fermions could have other spin values, but only what arises from adding, in the proper way, the elementary spins of their constituents.

By the 1960s, experiments had begun to show that protons were not actually fundamental particles at all, nor were neutrons for that matter. Theoretical models that built-up protons and neutrons and many other known particles called mesons and baryons soon led to the idea of the quark. For protons and neutrons, you needed three quarks, while for the mesons you only needed two of which one would be a quark and the other an anti-quark. The mathematics were impressive and elegant, and this system of quarks soon became the favored model for all particles that interacted through the strong nuclear force, itself produced by the exchanges of particles called gluons. Also in this scheme, quarks would be spin-1/2 fermions and the gluons would be spin-1 bosons much like the photons which carry light energy.

All seemed to be going great by the 1970s and 1980s. The quark model flourished, and many new subtle phenomena were uncovered through the application of what became the Standard Model of physics. But there was a fly in the ointment.

At first the explanation for how a proton could have a spin of ½ while at the same time being composed of three quarks, each also spin-1/2 particles, was pretty well settled. Because a proton consisted of two identical ‘up’ quarks and one ‘down’ quark, it was entirely reasonable that the two up quarks would have equal and opposite spin canceling each other out, leaving behind the down quark to carry the protons ½ unit of spin. Similarly for the neutron, its two down quarks combined to have a net-zero spin leaving the single up quark to carry the ½ unit of spin for the neutron.

The Proton Spin Crisis

All seemed to be well until experiments in 1987 at the European Muon Collaboration actually used carefully prepared beams of particles called muons to probe the interior of protons and double-check the way the quark spins were oriented with the protons spin. What they found was startling. Not more than 25% of the proton’s spin was generated by the quarks at all. The remaining 75% of what defines the spin of a proton had to come from some other source!

When you look at the mass of a proton compared to the masses of the three constituent quarks you discover something very fascinating. The masses of the quarks only account for about 1% of the mass of the entire proton. Instead, thanks to Einstein’s E=mc2, it is the stress energy of the gluon fields inside the proton that contribute the missing 99%. The mass that you read on the bathroom scale is only 1% contributed by the mass of your elementary quarks in grams, but 99% by the invisible energy(mass) of the gluon fields that occupy nuclear space!

Now for proton spin, the only other things rattling around inside the intense fields in the interior of a proton were the gluons holding the quarks together, and an ephemeral sea of quark-antiquark pairs that momentarily appeared and disappeared in the vacuum of space found there. This sea of vacuum or ‘virtual’ particles is absolutely required by modern quantum physics, and although we can never detect their comings and goings by any direct observation, we can detect their influence on nearby elementary particles.

In 2014, experiments at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven, New York collided polarized protons together and physicists think they have found a large part of the remainder of the protons spin. Perhaps 40% to 50% seems to be contributed by the gluons themselves. This still leave about 25% in some other source. Meanwhile, other experiments by MIT physicists determined that any anti-quarks produced inside a proton among the virtual quark sea contribute very little to the over-all spin of the proton.

When the experimental constraints are added up, we still do not have a precise measure of how the various proton constituents add up to give the universally constant spin of 1/2 to a proton that is observed for all protons to many decimal places.

Who would have thought that such an important number as ‘1/2’ arises from combining a number of messy phenomena that themselves seem imprecise!

When we think about the Big Bang we tend only to look at the first few instants when we think all of the mysterious and exciting action occurred. But actually, the first BILLION years are the real stars of this story!

What we understand today is not merely based on theoretical expectations. Thanks to specific observations during the last decade, we have actually discovered distant objects that help us probe critical moments during this span of time.

Infancy

By the end of the first 10 minutes after the Big Bang, the universe was filled with a cooling plasma of hydrogen and helium nuclei and electrons – too hot to come together to form neutral atoms at seething temperatures over 100 million Celsius. The traces that we do see of the fireball light from the Big Bang are called the cosmic background radiation, and astronomers have been studying it since the 1960s. Today, the temperature is 2.726 kelvins, but at one part in 100,000 there are irregularities in its temperature across the entire sky detected by the COBE, WMAP and Planck satellites and shown below. These irregularities are the gravitational fingerprints of vast clusters of galaxies that formed in the infant universe after several more billion years.

By 379,000 years, matter had cooled down to the point where electrons could bond with atomic nuclei to form neutral atoms of hydrogen and helium. For the first time in cosmic history, matter could go its own way and no longer be affected by the fireball radiation, which used to blast these assembled atoms apart faster than they could form. If you were living at this time, it would look like you were standing inside the surface of a vast dull-red star steadily fading to black as the universe continued to expand, and the gas steadily cooled over the millennia. No matter where you stood in the universe at this time, all you would see around you is this dull-red glow across the sky.

6 million years – By this time, the cosmic gas has cooled to the point that its temperature was only 500 kelvins (440 F). At these temperatures, it no longer emits any visible light. The universe is now fully in what astronomers call The Cosmic Dark Ages. If you were there and looking around, you would see nothing but an inky blackness no matter where you looked! With infrared eyes, however, you would see the cosmos filled by a glow spanning the entire sky.

20 million years – The hydrogen-helium gas that exists all across the universe is starting to feel the gravity effects of dark matter, which has started to form large clumps and vast spiders-web-like networks spanning the entire cosmos, with a mass of several trillion times the mass of our sun. As the cold, primordial gas falls into these gravity wells, it forms what will later become the halos of modern-day galaxies. All of this hidden under a cloak of complete darkness because there was as yet no physical objects in existence to light things up. Only detailed supercomputer simulations can reveal what occurred during this time.

The First Stars

100 million years – Once the universe got cold enough, large gas clouds stopped being controlled by their internal pressure, and gravity started to take the upper hand. First the vast collections of matter destined to become the haloes of galaxies formed. Then, or at about the same time, the first generation of stars appeared in the universe. These Population III stars made from nearly transparent hydrogen and helium gas were so massive, they lived for only a few million years before detonating as supernova. As the universe becomes polluted with heavier elements from billions of supernovae, collapsing clouds become more opaque to their own radiation, and so the collapse process stops when much less matter has formed into the infant stars. Instead of only producing massive Population III stars with 100 times our sun’s mass, numerous stars with masses of 50, 20 and 5 times our sun’s form with increasing frequency. Even smaller stars like our own sun begin to appear by the trillions. Most of this activity is occurring in what will eventually become the halo stars in modern galaxies like the Milky Way. The vast networks of dark matter became illuminated from within as stars and galaxies began to form.

200 million years – The oldest known star in our Milky Way called SM0313 formed about this time. This star contains almost no iron — less than one ten millionth of the iron found in our own Sun. It is located 6000 light years from Earth. Another star called the Methusela Star is located about 190 light years from Earth and was formed about the same time as SM0313.

The First Quasars and Black Holes

300 million years The most distant known ‘quasar’ is called APM 8279+5255, and contains traces of the element iron. This means that at about this time after the Big Bang, some objects are powered by enormous black holes that steadily consume a surrounding disk of gas and dust. For APM 8279+5255, the mass of this black hole is about 20 billion times more massive than the Sun. Astronomers do not know how a black hole this massive could gave formed so soon after the Big Bang. A dimple division shows that a 20 billion solar mass black hole forming in 300 million years would require a growth rate higher than 60 solar masses a year!

The First Galaxies

400 million years – The cold primordial matter becomes clumpy under the action of its own gravity. These clumps have masses of perhaps a few billion times our sun or less, and over time this material starts to collapse locally into even smaller clouds that become mini-galaxies where intense episodes of star formation activity are playing out.

This image shows the position of the most distant galaxy discovered so far with the Hubble Space Telescope. The remote galaxy GN-z11 shown in the inset is actually ablaze with bright young blue stars. They look red in this image because the wavelengths of light have been stretched by the expansion of the universe to longer, redder wavelengths. Like the images of so many other young galaxies, we cannot see individual stars, but their irregular shapes show that the stars they contain are spread out in irregular clumps within their host galaxy, possibly because they are from separate, merging clouds whose collisions have triggered the star-forming activity we see.

Although it is hard work, astronomers can detect the faint reddish traces of dozens of other infant galaxies such as MACS0647-JD, UDFj-39546284 and EGSY-2008532660. These are all small dwarf galaxies over 100 times less massive than our Milky Way. They are all undergoing intense star forming activity between 400 and 600 million years after the Big Bang.

The Gamma-Ray Burst Era begins about 630 million years after the Big Bang. Gamma-ray bursts are caused by very massive stars, perhaps 50 to 100 times our own sun’s mass, that explode as hypernovae and form a single black hole, so we know that these kinds of stars were already forming and dying by this time. Today from ‘across the universe’ we see these events occur about once each day!

800 million years – The quasar ULAS J1120+0641 is another young case of a supermassive black hole that has formed, and by this time is eating its surrounding gas and stars at a prodigious rate. The mass of this black hole is about 2 billion times the mass of our sun, and like others is probably the result of frequent galaxy mergers and rapid eating of surrounding matter.

Also at around this time we encounter the Himiko Lyman Alpha Blob; one of the most massive objects ever discovered in the early universe. It is 55,000 light-years across, which is half of the diameter of the Milky Way. Objects like Himiko are probably powered by an embedded galaxy that is producing young massive stars at a phenomenal rate of 500 solar masses per year or more.

Again the most brilliant objects we can see from a time about 900 million years after the big bang includes galaxies like SDSS J0100+2802 with a luminosity 420 trillion times that of our own Sun. It is powered by a supermassive black hole 12 billion times the mass of our sun.

The Re-Ionization Era

960 million years – By this time, massive stars in what astronomers call ‘Population III’ are being born by the billions across the entire universe. These massive stars emit almost all of their light in the ultraviolet part of the visible spectrum. There are now so many intense sources of ultraviolet radiation in the universe that all of the remaining hydrogen gas becomes ionized. Astronomers call this the Reionization Era. Within a few hundred million years, only dwarf galaxy-sized blobs of gas still remain and are being quickly evaporated. We can still see the ghosts of these clouds in the light from very distant galaxies. The galaxy SSA22-HCM1 is the brightest of the objects called ‘Lyman-alpha emitters’. It may be producing new stars at a rate of 40 solar masses per year and enormous amounts of ultraviolet light. The galaxy HDF 4-473.0 also spotted at this age is only 7,000 light years across. It has an estimated star formation rate of 13 solar masses per year.

1 billion years First by twos and threes, then by dozens and hundreds, clusters of galaxies begin to form as the gravity of matter pulls the clumps of galaxy-forming matter together. This clustering is speeded up by the additional gravity provided by dark matter. In a universe without dark matter, the number of clusters of galaxies would be dramatically smaller.

Clusters of Galaxies Form

Proto-galaxy cluster AZTEC-3 consists of 5 smaller galaxy-like clumps of matter, each forming stars at a prodigious rate. We now begin to see how some of the small clumps in this cluster are falling together and interacting, eventually to become a larger galaxy-sized system. This process of cluster formation is now beginning in earnest as more and more of these ancient clumps fall together under a widening umbrella of gravity. Astronomers are discovering more objects like AzTEC-3, which is the most distant known progenitor to modern elliptical galaxies. By 2.2 billion years after the Big Bang, it appears that half of all the massive elliptical galaxies we see around us today have already formed by this time.

Thanks to the birth and violent deaths of generations of massive Population III stars, the universe is now flooded with heavy elements such as iron, oxygen, carbon and nitrogen: The building blocks for life. But also elements like silicon, iron and uranium which help to build rocky planets and heat their interiors. The light from the quasar J033829.31+002156.3 can be studied in detail and shows that by this time, element-building through supernova explosions of Population III stars has produced lots of carbon, nitrogen and silicon. The earliest planets and life forms based upon these elements now have a chance to appear in the universe. Amazingly, we have already spotted such an ancient world!

Earliest Planets Form

At 1 billion years after the Big Bang, the oldest known planet PSR B1620-26 b has already formed. Located in the globular cluster Messier-4, about 12,400 light-years from Earth, it bears the unofficial nicknames “Methuselah” and “The Genesis Planet” because of its extreme age. The planet is in orbit around the two very old stars: A dense white dwarf and a neutron star. The planet has a mass of 2.5 times that of Jupiter, and orbits at a distance a little greater than the distance between Uranus and our own Sun. Each orbit of the planet takes about 100 years.

Wonders to Come!

Although the Hubble Space Telescope strains at its capabilities to see objects at this early stage in cosmic history, the launch of NASA’s Webb Space Telescope will uncover not dozens but thousands of these young pre-galactic objects with its optimized design. Within the next decade, we will have a virtually complete understanding of what happened during and after the Cosmic Dark Ages when the earliest possible sources of light could have formed, and one can only marvel at what new discoveries will turn up.

Something weird is going on in the universe that is causing astronomers and physicists to lose a bit of sleep at night. You have probably heard about the discovery of dark energy and the accelerating expansion of the universe. This is a sign that something is afoot that may not have a pleasant outcome for our universe or the life in it.

Big Bang Cosmology V 1.0

The basic idea is that our universe has been steadily expanding in scale since 14 billion years ago when it flashed into existence in an inconceivably dense and hot explosion. Today we can look around us and see this expansion as the constantly- increasing distances between galaxies embedded in space. Astronomers measure this change in terms of a single number called the Hubble Constant which has a value of about 70 km/sec per megaparsecs. For every million parsecs of separation between galaxies, a distance of 3.24 million light years, you will see distant galaxies speeding away from each other at 70 km/sec . This conventional Big Bang theory has been the main-stay of cosmology for decades and it has helped explain everything from the formation of galaxies to the abundance of hydrogen and helium in the universe.

Big Bang Cosmology V 2.0

Beginning in the 1980’s, physicists such as Alan Guth and Andre Linde added some new physics to the Big Bang based on cutting-edge ideas in theoretical physics. For a decade, physicists had been working on ways to unify the three forces in nature: electromagnetism, and the strong and weak nuclear forces. This led to the idea that just as the Higgs Field was needed to make the electromagnetic and weak forces look different rather than behave as nearly identical ‘electroweak’ forces, the strong force needed its own ‘scalar field’ field to break its symmetry with the electroweak force.

When Guth and Linde added this field to the equations of Big Bang cosmology they made a dramatic discovery. As the universe expanded and cooled, for a brief time this new scalar field made the transition between a state where it allowed the electroweak and strong forces to look identical, and a state where this symmetry was broken representing the current state of affairs. This period of time extended from about 10(-37) second to 10(-35) seconds; a mere instant in cosmic time, but the impact of this event was spectacular. Instead of the universe expanding at a steady rate in time as it does now, the separations between particles increased exponentially in time in a process called Inflation. Physicists now had a proper name for this scalar field: The Inflaton Field.

Observational cosmology has been able to verify since the 1990s that the universe did, indeed, pass through such an inflationary era at about the calculated time. The expansion of space at a rate many trillions of times faster than the speed of light insured that we live in a universe that looks as ours does, especially in terms of the uniformity of the cosmic ‘fireball’ temperature. It’s 2.7 kelvins no matter where you look, which would have been impossible had the Inflationary Era not existed.

Physicists consider the vacuum of space to be more than ‘nothing’. Quantum mechanically, it is filled by a patina of particles that invisibly come and go, and by fields that can give it a net energy. The presence of the Inflaton Field gave our universe a range of possible vacuum energies depending on how the field interacted with itself. As with other things in nature, objects in a high-energy state will evolve to occupy a lower-energy state. Physicists call the higher-energy state the False Vacuum and the lower-energy state the True Vacuum, and there is a specific way that our universe would have made this change. Before Inflation, our universe was in a high-energy, False Vacuum state governed by the Inflaton Field. As the universe continued to expand and cool, a lower-energy state for this field was revealed in the physics, but the particles and fields in our universe could not instantaneously go into that lower-energy state. As time went on, the difference in energy between the initial False Vacuum and the True Vacuum continued to increase. Like bubbles in a soda, small parts of the universe began to make this transition so that we now had a vast area of the universe in a False Vacuum in which bubbles of space in the True Vacuum began to appear. But there was another important process going on as well.

When you examine how this transition from False to True Vacuum occurred in Einstein’s equations that described Big Bang cosmology, a universe in which the False Vacuum existed was an exponentially expanding space, while the space inside the True Vacuum bubbles was only expanding at a simple, constant rate defined by Hubble’s Constant. So at the time of inflation, we have to think of the universe as a patina of True Vacuum bubbles embedded in an exponentially-expanding space still caught in the False Vacuum. What this means for us today is that we are living inside one of these True Vacuum bubbles where everything looks about the same and uniform, but out there beyond our visible universe horizon some 14 billion light years away, we eventually enter that exponentially-expanding False Vacuum universe. Our own little bubble may actually be billions of times bigger than what we can see around us. It also means that we will never be able to see what these other distant bubbles look like because they are expanding away from us at many times the speed of light.

Big Bang Cosmology 3.0

You may have heard of Dark Energy and what astronomers have detected as the accelerating expansion of the universe. By looking at distant supernova, we can detect that since 6 billion years after the Big Bang, our universe has not been expanding at a steady rate at all. The separations between galaxies has been increasing at an exponential rate. This is caused by Dark Energy, which is present in every cubic meter of space .The more space there is as the universe expands, the more Dark Energy and the faster the universe expands. What this means is that we are living in a False Vacuum state today in which a new Inflaton Field is causing space to dilate exponentially. It doesn’t seem too uncomfortable for us right now, but the longer this state persists, the greater is the probability our corner of the universe will see a ‘bubble’ of the new True Vacuum appear. Inside this bubble there will be slightly different physics such as the mass of the electron or the quark may be different. We don’t know when our corner of the universe will switch over to its True Vacuum state. It could be tomorrow or 100 billion years from now. But there is one thing we do know about this progressive, accelerated expansion.

Eventually, distant galaxies will be receding from our Milky Way at faster that the speed of light as they are helplessly carried along by a monstrously-dilating space. This also means they will become permanently invisible for the rest of eternity as their light signals never keep pace with the exponentially-increasing space between them. Meanwhile, our Milky Way will become the only cosmic collection of matter we will ever be able to see from then on. It is predicted that this situation will occur about 100 billion years from now when the Andromeda Galaxy will pass beyond this distant horizon.

As for what the new physics will be in the future True Vacuum state is anyone’s guess. If the difference in energy between the False and True vacuum is only a small fraction of the mass of a neutrino (a few electron-Volts) we may hardly know that it happened and life will continue. But if it is comparable to the mass of the electron (512,000 eV), we are in for some devastating and fatal surprises best not contemplated.

Back in the 1800’s, Ludwig Boltzmann (1844-1906) developed the idea of entropy and thermodynamics, which have been the main-stay of chemistry and physics ever since. Long before atoms were identified, Boltzmann had used them in designing his theory of statistical mechanics, which related entropy to the number of possible statistical states these particles could occupy. His famous formula

S = k log W

is even inscribed on his tombstone! His frustrations with the anti-atomists who hated his crowning achievement ‘statistical mechanics’ led him in profound despair to commit suicide in 1906.

If you flip a coin 4 times, it is unlikely that all 4 flips will result in all-heads or all-tails. It is far more likely that you will get a mixture of heads and tails. This is a result of their being a total of 2^4 = 16 possible outcomes or ‘states’ for this system, and the state with all heads or all tails occur only 1/16 of the time. Most of the states you will produce have a mixture of heads and tails (14/16). Now replace the coin flips by the movement of a set of particles in three dimensions.

Boltzmann’s statistical mechanics related the number of possible states for N particles moving in 3-dimensional space, to the entropy of the system. It is more difficult to calculate the number of states than for the coin flip example above, but it can be done using his mathematics, and the result is the ‘W’ in his equation S = k Log W. The bottom line is that, the more states available to a collection of particles (for example atoms of a gas), the higher is the entropy given by . How does a gas access more states? One way is for you to turn up its temperature so that the particles are moving faster. This means that as you increase the temperature of a gas, its entropy increases in a measurable way.

Cosmologically, as our universe expands and cools, its entropy is actually increasing steadily because more and more space is available for the particles to occupy even as they are moving more slowly as the temperature declines. The Big Bang event itself, even at its unimaginably high temperature was actually a state of very low entropy because even though [particles were moving near the speed of light, there was so little space for matter to occupy!

For random particles in a gas colliding like billiard balls, with no other organizing forces acting on them, (called the kinetic theory of gases), we can imagine a collection of 100 red particles clustered in one corner of a box, and 1000 other blue particles located elsewhere in the box. If we were to stumble on a box of 1100 particles that looked like this we would immediately say ‘how odd’ because we sense that as the particles jostled around the 100 red particles would quickly get uniformly spread out inside the box. This is an expression of their being far more available states where the red balls are uniformly mixed, than states where they are clustered together. This is also a statement that the clustered red balls is a lower-entropy version of the system, and the uniformly-mixed version is a higher form of entropy. So we would expect that the system evolves from lower to higher entropy as the red particles diffuse through the box: Called the Second Law of Thermodynamics.

Boltzmann Brains.

The problem is that given enough time, even very rare states can have a non-zero probability of happening. With enough time and enough jostling, we could randomly find the red balls once again clustered together. It may take billions of years but there is nothing that stands in the way of this happening from statistical principles. Now let’s suppose that instead of just a collection of red balls, we have a large enough system of particles that some rare states resemble any physical object you can imagine: a bacterium, a cell phone, a car…even a human brain!

A human brain is a collection of particles organized in a specific way to function and to store memories. In a sufficiently large and old universe, there is no obvious reason why such a brain could not just randomly assemble itself like the 100 red particles in the above box. It would be sentient, have memories and even senses. None of its memories would be of actual events it experienced but simply artificial reconstructions created by just the right neural pathways randomly assembled. It would remember an entire lifetime to date without having actually lived or occupied any of the events in space and time.

When you calculate the probability for such a brain to evolve naturally in a low-entropy universe like ours rather than just randomly assembling itself you run into a problem. According to Boltzmann’s cosmology, our vast low-entropy and seemingly highly organized universe is embedded in a much larger universe where the entropy is much higher. It is far less likely that our organized universe exists in such a low entropy state conducive to organic evolution than a universe where a sentient brain simply assembles itself from random collisions. In any universe destined to last for eternity, it will rapidly be populated by incorporeal brains rather than actual sentient creatures! This is the Paradox of the Boltzmann Brain.

Even though Creationists like to invoke the Second Law to deny evolution as a process of random collisions, the consequence of this random idea about structure in the universe says that we are actually all Boltzmann Brains not assembled by evolution at all. It is, however, of no comfort to those who believe in God because God was not involved in randomly assembling these brains, complete with their own memories!

So how do we avoid filling our universe with the abomination of these incorporeal Boltzman Brains?

The Paradox Resolved

First of all, we do not live in Boltzmann’s universe. Instead of an eternally static system existing in a finite space, direct observations show that we live in an expanding universe of declining density and steadily increasing entropy.

Secondly, it isn’t just random collisions that dictate the assembly of matter (a common idea used by Creationists to dismantle evolution) but a collection of specific underlying forces and fundamental particles that do not come together randomly but in a process that is microscopically determined by specific laws and patterns. The creation of certain simple structures leads through chemical processes to the inexorable creation of others. We have long-range forces like gravity and electromagnetism that non-randomly organize matter over many different scales in space and time.

Third, we do not live in a universe dominated by random statistical processes, but one in which we find regularity in composition and physical law spanning scales from the microscopic to the cosmic, all the way out to the edges of the visible universe. When two particles combine, they can stick together through chemical forces and grow in numbers from either electromagnetic or gravitational forces attracting other particles to the growing cluster, called a nucleation site.

Fourth, quantum processes and gravitational processes dictate that all existing particles will eventually decay or be consumed in black holes, which will evaporate to destroy all but the most elementary particles such as electrons, neutrinos and photons; none of which can be assembled into brains and neurons.

The result is that Boltzmann Brains could not exist in our universe, and will not exist even in the eternal future as the cosmos becomes more rarefied and reaches its final and absolute thermodynamic equilibrium.

The accelerated expansion of the universe now in progress will also insure that eventually all complex collections of matter are shattered into individual fundamental particles each adrift in its own expanding and utterly empty universe!

The Big Bang theory says that the entire universe was created in a tremendous explosion about 14 billion years ago. The enormity of this event is hard to grasp and it seems natural to ask ourselves ‘What was it like then?’ and ‘What happened before the Big Bang?’.

Thanks to what physicists call the Standard Model, we have a detailed understanding of quantum physics, matter, energy and force that let us reproduce what the universe looked like as early as a billionth of a second after the Big Bang. The results of high-precision observational cosmology also let us verify that the Standard Model predictions match what we see as the general properties of the matter and energy in our universe up until this unimaginable time. We can actually go a bit farther back towards the beginning thanks to detailed studies of the cosmic background radiation!

At a time 10(-36) second ( that is a trillionth of a trillionth of a trillionth of a second!) after the Big Bang, a spectacular change in the size of the universe occurs. This is the Inflationary Era when the strong nuclear force becomes distinguishable from the weak and electromagnetic forces. The temperature is an incredable 10 thousand trillion trillion degrees and the density of matter has sored to nearly 10(75) gm/cm3. This number is so enormous even our analogies are almost beyond comprehension. At these densities, the entire Milky Way galaxy could easily be stuffed into a volume no larger than a single hydrogen atom!

Between a billionth of a second and 10(-35) seconds is a No Man’s Land currently in accessible to our technology and requires instruments such as the CERN Large Hadron Collider scaled up to the size of our solar system or even larger! This is also the domain of the so-called Particle Desert that I previously wrote about, and the landscape of the predictions made by supersymmetric string theory, for which there is as yet no evidence of their correctness despite decades of intense theoretical research.

THROUGH A LOOKING GLASS, DARKLEY

Since our technology will not allow us to physically reproduce the conditions during these ancient times, we must use our mathematical theories of how matter behaves to mentally explore what the universe was like then. We know that the appearence of the universe before 10(-43) second can only be adequatly described by modifying the Big Bang theory because this theory is, in turn, based on the General Theory of Relativity. At the Planck Scale, we need to extend General Relativity so that it includes not only the macroscopic properties of gravity but also is microscopic characteristics as well. The theory of ‘Quantum Gravity’ is still far from completion but physicists tend to agree that there are some important quide-posts to help us understand how it applies to Big Bang theory.

QUANTUM COSMOLOGY

In the language of General Relativity, gravity is a consequence of the deformati on of space caused by the presence of matter and energy. In Quantum Gravity theory, gravity is produced by massless gravitons, or strings (in what is called string theory), or loops of energy (in what is called loop quantum gravity), so that gravitons now represent individual packages of curved space.

The appearence and dissappearence of innumerable gravitons gives the geometry of space a very lumpy and dynamic appearance. The geometry of space twists and contorts so that far flung regions of space may suddenly find themselves connected by ‘wormholes’ and quantum black holes, which constantly appear and dissappear within 10(-43) seconds. The geometry of space at a given moment will have to be thought of as an average over all 3-dimensional space geometries that are possible.

What this means is that we may never be able to calculate with any certainty exactly what the history of the universe was like before 10(-43) seconds. To probe the history of the universe then would be like trying to trace your ancestral roots if every human being on earth had a possibility of being one of your parents. Now try to trace your family tree back a few generations! An entirely new conception of what we mean by ‘a history for the universe’ will have to be developed. Even the concepts of space and time will have to be completely re-evaluated in the face of the quantum fluctuations of spacetime at the Planck Era!

Now we get to a major problem in investigating the Planck Era.

BUT WAIT…THERE’S MORE!

Typically we make observations in nuclear physics by colliding particles and studying the information created in the collision, such as the kinds of particles created, their energy, momentum, spin and other ‘quantum numbers’. The whole process of testing our theories relies on studying the information generated in these collisions, searching for patterns, and comparing them to the predictions. The problem is that this investigative process breaks down as we explore the Planck Era. When the quantum particles of space (gravitons, strings or loops)collide at these enormous energies and small scales, they create quantum black holes that immediately evaporate. You cannot probe even smaller scales of space and time because all you do is to create more quantum black holes and wormholes. Because the black holes evaporate into a randomized hailstorm of new gravitons you cannot actually make observations of what is going on to search for non-random patterns the way you do in normal collisions!

Quantum Gravity, if it actually exists as a theory, tells us that we have finally reached a theoretical limit to how much information we can glean about the Planck Era. Our only viable options involve exploring the Inflationary Era and how this process left its fingerprints on the cosmic background radiation through the influence of gravitational waves.

Fortunately, we now know that gravity waves exist thanks to the discoveries by the LIGO instrument in 2016. We also have indications of what cosmologists call the cosmological B-Modes which are the fingerprints of primordial gravity waves interacting with the cosmic background radiation during the Inflationary Era.

We may not be able to ever study the Planck Era conditions directly when the universe was only 10(-43) seconds old, but then again, knowing what the universe was doing 10(-35) seconds after the Big Bang all the way up to the present time is certainly an impressive human intellectual and technological success!

Today, physicists are both excited and disturbed by how well the Standard Model is behaving, even at the enormous energies provided by the CERN Large Hadron Collider. There seems to be no sign of the expected supersymmetry property that would show the way to the next-generation version of the Standard Model: Call it V2.0. But there is another ‘back door’ way to uncover its deficiencies. You see, even the tests for how the Standard Model itself works are incomplete, even after the dramatic 2012 discovery of the Higgs Boson! To see how this backdoor test works, we need a bit of history.

Glueballs found in a quark-soup (Credit: Alex Dzierba, Curtis Meyer and Eric Swanson)

Over fifty years ago in 1964, physicists Murray Gell-Mann at Caltech and George Zweig at CERN came up with the idea of the quark as a response to the bewildering number of elementary particles that were being discovered at the huge “atom smasher” labs sprouting up all over the world. Basically, you only needed three kinds of elementary quarks, called “up,” “down” and “strange.” Combining these in threes, you get the heavy particles called baryons, such as the proton and neutron. Combining them in twos, with one quark and one anti-quark, you get the medium-weight particles called the mesons. In my previous blog, I discussed how things are going with testing the quark model and identifying all of the ‘missing’ particles that this model predicts.

In addition to quarks, the Standard Model details how the strong nuclear force is created to hold these quarks together inside the particles of matter we actually see, such as protons and neutrons. To do this, quarks must exchange force-carrying particles called gluons, which ‘glue’ the quarks together in to groups of twos and threes. Gluons are second-cousins to the photons that transmit the electromagnetic force, but they have several important differences. Like photons, they carry no mass, however unlike photons that carry no electric charge, gluons carry what physicist call color-charge. Quarks can be either ‘red’, ‘blue’ or ‘green’, as well as anti-red, anti-green and anti-blue. That means that quarks have to have complex color charges like (red, anti-blue) etc. Because the gluons carry color charge, unlike photons which do not interact with each other, gluons can interact with each other very strongly through their complicated color-charges. The end result is that, under some circumstances, you can have a ball of gluons that resemble a temporarily-stable particle before they dissipate. Physicists call these glueballs…of course!

Searching for Glueballs.

Glueballs are one of the most novel, and key predictions of the Standard Model, so not surprisingly there has been a decades-long search for these waifs among the trillions of other particles that are also routinely created in modern particle accelerator labs around the world.

Example of glueball decay into pi mesons.

Glueballs are not expected to live very long, and because they carry no electrical charge they are perfectly neutral particles. When these pseudo-particles decay, they do so in a spray of other particles called mesons. Because glueballs consist of one gluon and one anti-gluon, they have no net color charge. From the various theoretical considerations, there are 15 basic glueball types that differ in what physicists term parity and angular momentum. Other massless particles of the same general type also include gravitons and Higgs bosons, but these are easily distinguished from glueball states due to their mass (glueballs should be between 1 and 5GeV) and other fundamental properties. The most promising glueball candidates are as follows:

By 2015, the f-zero(1500) and f-zero(1710) had become the prime glueball candidates. The properties of glueball states can be calculated from the Standard Model, although this is a complex undertaking because glueballs interact with nearby quarks and other free gluons very strongly and all these factors have to be considered.

On October 15, 2015 there was a much-ballyhooed announcement that physicists had at last discovered the glueball particle. The articles cited Professor Anton Rebhan and Frederic Brünner from TU Wien (Vienna) as having completed these calculations, concluding that the f-zero(1710) was the best candidate consistent with experimental measurements and its predicted mass. More rigorous experimental work to define the properties and exact decays of this particle are, even now, going on at the CERN Large Hadron Collider and elsewhere.

So, between the missing particles I described in my previous blog, and glueballs, there are many things about the Standard Model that still need to be tested. But even with these predictions confirmed, physicists are still not ‘happy campers’ when it comes to this grand theory of matter and forces. Beyond these missing particles, we still need to have a deeper understanding of why some things are the way they are, and not something different.